How do I get over my insecurities in our relationship?

September will be two years off and on for my boyfriend and I. Here recently we have gotten more serious then we ever have been. He's mentioned getting engaged and even took me looking at houses with him and on the way home he pointed to a church where he said we could get married at. Every girls dream right? Have the love of your life throw out hints that he's ready for the next step in the relationship. I have dreamed of getting married since I was a little girl but now that it's out in the open and something that could actually happen in my near future I'm feeling insecure with myself and in our relationship. I find myself not feeling good enough and questioning him if he doesn't text me back within a certain amount of time...dumb right?! As dumb as I know it is I can't help it. It's like I've got all kinds of anxiety going on that I can't get rid of. I also find myself feeling not as pretty or as skinny as some other girls which I shouldn't feel that way at all! I should actually feel good about myself. I recently went from 161 lbs to 135, so it baffles me. The only thing I can think of is that I finally have a good thing and exactly what I want is in the pathway of happening and I'm scared of losing it? Idk. Help!