For the past month I have frequently been feeling either depressed/anxious or really happy, but I'm not sure whether this is a normal thing considering the situation I'm in.

A brief background:
I'm 27 and my last boyfriend was in my sophomore year of high school. We only went out for 3 months and didn't even kiss each other. Since then what has usually happened is that the guys I am interested in are never interested in me or I'm not interested the guys that are into me.

Now, I started dating a guy about a month ago that I like A LOT. Strangely, he seems to be into me too. Because this is new territory for me I constantly get anxious about whether we will eventually become more than just dating. Sometimes I get so depressed thinking about how we might not work out. I would be crushed. Sometimes I find myself talking myself out of liking him just so that when it doesn't work out it won't hurt as bad. I hate thinking these things. I want nothing more than to be with this guy.

Previously, I had accepted the fact that I would probably be single the rest of my life. I am a loner and don't put myself out there that much. I just thought that that was how my life was going to be. However, now that I have been dating this guy being alone is the last thing I want. I thought possibly falling in love would be a terrible thing, but now that is what I want more than ever. How do I get myself to stop thinking the worst? Sometimes I make myself so depressed and just assume he doesn't like me. Then I see him and we have a great time together and I feel great, only to have that worrying come back hours later. This is driving me crazy. What can I do?