You are normal but like most of us you lack self discipline and control of your thoughts and feelings, especially in the sexuality department.
I'm of the opinion that feelings shouldn't be suppressed. At the same time, they need to be under some control. The first step (which you are making) is to be aware that they exist and what they are.
Suppressing them (to my mind) means pushing them back to a place where we're not aware of them. The problem with that is we can't be in control of something we're unaware of in ourselves. These emotional forces may continue to drive or at least influence our actions but we don't see that.
What might be helpful is to realize that the feelings that you associate with men you find 'unavailable' (to you) are one thing, the obsession with them is another. The first you might not be able to control, at least not until you've fully explored where they come from. What is the fascination with, or attraction to, men who are emotionally unavailable to you? That is a deep psychological question and I'd be suspect of any 'too easy' answer. Still, it is one worth putting on the 'back burner' of your mind, letting it sort of 'cook' there so it becomes a question you ask yourself from time to time and see what 'answer' comes up. Likely this will change through time and experience (and, if you go there, therapy with a professional guide).
The obsessive tendency is the real immediate problem. Like you suggest, it can make you feel 'crazy', like your life, especially your feelings, are not under your control. This is true, they're not! We feel what we feel for whatever reason or no reason at all.
But obsessing about them is a choice. It doesn't seem that way when we're in the midst of it. One of my mottoes is, "Our lives are determined by what we pay attention to." Followed up with, "The quality of our lives is determined by the quality of our attention to them."
So the first step is to see and acknowledge this obsessive tendency and look at it. Pay attention to it, how it is motivating you to think or do certain things. If you're following me here, this 'paying attention to it' itself is a shift of attention. Now you're not looking at the other guy so much, you're looking at yourself, what is going on inside you.
This is where the possibility of choice comes in. Focusing your attention on your own feelings, seeing how obsessing about someone else is taking you away from your own life, your own awareness of yourself, is a key.
I'm not sure how it will work for you but when I find myself in a situation like this I ask myself, why am I doing this to myself? Why make myself miserable wanting something I can't have? It isn't easy but if I sort of 'stay with' those kinds of questions, focusing my attention on myself this way, I begin to think less about 'the other guy' and more about taking care of my own needs. I don't 'need' to 'obsess' over anyone (or any 'thing' for that matter). What I need is to see what my needs are, accept them, and see if it is possible to meet them.
It may not be possible right now! I may 'need' a lover but maybe I'm not really ready for that because I haven't first figured out how to meet my own needs without one. Thus, I displace or project my own emotional needs onto someone else, as if they can fix or fulfill them.
For sure having a lover can meet certain needs but we have to be very careful here. A healthy relationship isn't only about getting *our own* needs met; it is about meeting one another's needs. It is inclusive, not exclusive. It's about 'what can we do for one another' not 'what can you do for me'.
I don't know if my words here can help. But the way I see it, for the most part, my needs are my own and I need to meet as many of them as I can. To do that I need to pay attention to them, see what ones I can meet, feel the loss of those I can't (a kind of suffering I accept as inevitable to some extent). I also ask myself the question, can I 'be there' for anyone else? Can I be aware of his needs and help him meet them? If, for example, the 'need' is just for a sexual outlet then perhaps that is possible right here, right now. If it is for something deeper, something emotional, a sense of 'security' for example, there are going to be a lot more variables. How 'secure' do I feel in myself? If I'm feeling insecure, I can't very well be a 'rock' for someone else's insecurities. (Again, this is just an example.)
Anyway, the key to getting beyond obsession is to first be aware of it and give it some attention. It is an important, significant inner dynamic, worthy of our awareness. Beyond that it is just a matter of beginning to choose *where* we want to place our attention. If we're so caught up in focusing on someone else that we're loosing ourselves, well, that isn't healthy for us, is it? (It isn't healthy for them, either, btw.) So I say, "Ok, I'm obsessing, that isn't healthy, what else can I do?" I go for a walk. I look at things. I find my mind wandering back to the obsession. I say, woah, stop that, pay attention. Where are you? What are you doing? Stay here, be here now. Focus on what is right in front of you. What are you going to do next… etc.
This process takes time. I personally can't just 'shut it off'. BUT, with a bit of awareness and practice, eventually it becomes easier. The tight obsessive tangle of my thoughts and feelings begins to loosen so I can untie the knot. Finally, in time, I'm free.
Hope this helps.