Online relationships/ online a "cyphering" cheating?

Hello everyone I am in a long term relationship and I think my boyfriend may be cheating on me, but not in person it is with a girl he knows but it is online only, he only knows her online as well but they talk all the time only ually sometimes , so they are like online friends with benefits...... I feel horrible and definitely feel like he is cheating on me he thinks it is no big deal - am I wrong.? I mean I have no problem with or anything but this feel different - a lot different what is your opin cheating or not?