it's not because of that... It's because your desensitzing your penis from all the masturbation you're doing. Your penis so use to the feeling of your hand that it can't enjoy the feeling of the vagina. When you have sex with your gf, your penis should feel a great sensation the entire time, so strong that you feel like you can climax from thrusting real fast but you the entire you don't because you're holding back your climax. That's how sex should feel, condom or no condom.
How do I know this???? Well for years I had your problem. In fact, I would lose my erection during sex.
I decided to leave my penis alone for an entire month (but I still watch porn/just don't masturbate) and after that month I was feigning for my gf to touch my penis. And when she did, It felt awesome. I felt like I was being taken advantage of. She then gave me oral sex and that felt more sensitive than it normally do. Then I put on the condom and slid in her vagina and that felt more sensitive than it normally do. I felt the need to climax for 15 minutes straight but I held it back. She finally told me I can let it out so I did.... I haven't experience sex like that in a long time WITH A LATEX CONDOM. So I know my remedy works because I already tried it.
Refrain from masturbation, use only sensitive skin soap products to clean your penis, and let only your girlfriend touch your penis. Guarantee you will see great results my friend!
It's because of the Celexa. A lot of antidepressants can effect your sex life. Talk to your Dr about adding or switching you to another antidepressant like Cymbalta or Wellbutrin. They're in a different class than the SSRI's and don't cause the sexual problems like the SSRI's do. Remar