<human>: Give me the gist of the text in a nutshell

I am by no means trying to defend my actions, I just want to know if talking to my girl about it is a good idea. 
We told each other we had feelings for each other in August and then I asked her to formally be my girlfriend in October. We agreed that we both wanted to take things slow and we hadn't been a very serious couple. A lot of people thought we were just friends with benefits. We didn't go on many dates. We just spent a lot of time together and hooked up a lot. 
In November, I slept with another girl. My girlfriend was out of town and leading up to that night, I didn't feel like I was getting the attention/affection I wanted. A similar event happened in December, but this time, my girlfriend was in town, but she had blown me off.
At the time, I didn't consider us very serious. We were taking things slow, I didn't feel very invested in the whole thing and I didn't feel bad about cheating. But now we have a very strong relationship. We both love each other and we see a future together. I'm wondering if I should tell her. Can we have a truly healthy relationship with this lie in our past? Any advice?
<bot>: Cheated on my gf twice, b/c I didn't think we were very serious, now we are serious. Should I come clean?