The answer is simply yes. It is cheating because you are taking away from your partner and giving it to someone else. If you want to talk, share feelings, have fun, etc then you should be doing that with your partner. Your partner is special, as he or she is the only one who gets that privledge. If you are going around giving that to other people as well, then it's not special anymore and the relationship becomes meaningless and loses it's value. Things that are abundant and easily obtained are not valuable, rare things are valuable and you have an obligation to your partner to uphold that value. If you aren't getting enough attention, maybe you should break up with him instead of ruining your credibility by cheating.