How to overcome shyness when speaking to a guy?

Hi. I’m 21 years old and in need of some serious advice!!! This is embarrassing, but I’ve always had a problem with being too shy around a man I am interested in. This is a big problem for me because I feel like I end up being boring or too quiet which I’m scared will ultimately leave the man uninterested. I’m the sort of person who is a bit reserved when meeting new people. It takes me a little while to feel comfortable with a person enough to be myself. With men however, it’s even worse. With my ex boyfriend, it took quite a while for us to start dating and for him to have feelings for me because I took so long to show him who I really am. And now it’s happening again! Lately I’ve been very attracted to a friend my best friend just moved in with. I’ve been visiting a lot, and have found myself interested in getting to know him. His friend seems to be interested in me as well. I haven’t had a chance to really speak to him on a personal level because we are always with others, however last night he messages me over the internet, and even over the internet I freeze up and get nervous! I find myself thinking too much about what to say and end up not answering back in way too long, or saying something boring which doesn’t lead to a great conversation. I have a hard time relaxing and just going with the flow and being myself. I feel like I’m pretty likeable when I’m being myself, so it’s really a set back and gives the guy the wrong picture of who I am. I’m never usually so shy except in this type of situation. I would really appreciate some advice on how to get my nerves out of the way so I can be myself and carry on a normal conversation!!! Thanks. :P