Commitment issues

I tend to have a problem sometime around 2 months into the relationship and I start to feel suffocated and often times freaked out by how good a guy is to me. My longest relationship would be three months. I get so emotionally claustrophobic and I don't know how to bring it up without offending their feelings and I just suffer in silence until I can't take it anymore. But recently I've been in a good relationship with such a genuine guy who wants to plan a future with me and the nicer he is to me, the more I feel annoyed. And I don't want to break up and I don't want to screw this up, but I can't help feeling suffocated. Help