how to learn to develop libido?

I’m 24 years old (M), I’m not shy or insecure, I’m active in sports terms and have many possibilities for dates or sexual encounters. However, I have been noticing for quite some time that I have a problem with sexual desire, it is difficult for me to eroticize myself with girls, but not when I masturbate (and im sure im not lgbt). This would not be a problem if it were not for the fact that I consider it so. I really enjoy sexual encounters and yet somehow it’s hard for me to get into the “mood”. Even, for fear of failure, I do viagra on a few occasions and I am not proud of it. Does anyone know how I can find more ways to warm up? Excuse my english.