Is it normal to get boner from gf's pic?

So my girlfriend and I are both 18, and we have a long distance relationship (788 miles away). We've known each other since we were 13, and been dating since we were 15. We both drove half the distance and met each other in the middle last year, that's the only time we have been together in person. We've been talking about getting a place together some time, but we still need to get some money together.

Anyway, that day we were together we made out a lot, and my dick was so fucking hard, but I knew we just could't have sex the first time meeting.

We talk to each other on the phone at least once a week, and we text we other most of the day and night, and we always send each other pics. The first time she sent me a pic I got a stiffie, but as more days go by it just gets worse. It's gotten to the point that after we say goodnight I have to jack off because there's already pre cum dripping out of my dick. Everytime I think about her I get a boner. IIN? is there anyone out there with a similar situation?