Am I cheating on my girlfriend?

I have been in a long-distance relationship with a girl for two years. We used to live in the same city before I had to move, and we dated for almost a year, which makes this a three-year relationship. We love each other a lot, but the pressure of keeping things normal without seeing each other in person is starting to take a toll on me. A colleague of mine from the office recently asked me out for coffee and I agreed. We had a wonderful time and I genuinely enjoyed getting to know her. She wants me to go out to dinner with her now and I don’t know what her intentions are. I feel as if I am cheating on my girlfriend by meeting her, but a part of me also likes the idea because I miss being with someone. What should I do?
Why not go out to dinner after telling your girlfriend that you’re meeting a colleague, and explain to your colleague that you are in a committed long-distance relationship? Nothing prevents you from having a platonic relationship with this colleague who may end up being a good friend, and you shouldn’t feel as if you’re cheating just by meeting someone for dinner. Relationships are always about trust, and long-distance relationships rely on this even more. Be honest, make sure you state your intentions clearly, and don’t feel guilty for no reason. You haven’t done anything wrong.

How do I convince my partner to be more loving towards me? She is an amazing human being, but she just doesn’t behave in a manner that shows me how much she loves me. It’s just a personality trait, but I would like to change that if possible. 
You presumably fell in love with her because of her personality, not despite it. Trying to change someone is usually futile, but you can always try and be more specific about what you mean, so she understands your perspective a little better.