Responses
Well first loves are not always the ones that make you happy in the end. He can fall in love with another person and even be happier than he would've been with the first love.
But talking about this manga in particular, yes he's sabotaging his own love... But in a way it could be good. If the friend is really in love with him and it's not just interested (yep it can happen sadly) he will try to conquer him back. That would give him a boost of self-esteem and faith in the relationship maybe?
I firmly believe people sabotage their own happiness all the time.
You can tell he's so terrified of being loved because that means he might lose that love someday.
So instead of taking a chance, he'd rather just reject his chance at being with the person he loves with all his heart, in favor of being with someone who won't ever be able to truly break his heart, simply because they never really had it in the first place.