As a parent, remember the "Airplane Rule" -- taking care of yourself first is essential in helping you take better care of your children. Balancing parenting, relationship, work, and fun is difficult, but important.
So sure, going out with friends is great, and your daughter -- at this age -- can certainly handle having a babysitter a couple of times a month. But this sounds like it might be more of a relationship issue. Are you making enough time for your boyfriend? Are you two making each other a priority? Perhaps he feels worried or jealous about your going out? Does he fully understand your intentions and plans? Perhaps your dancing has him concerned about what else might go on while you're out dancing without him.
Taking care of your relationship with your significant other is an important part of the picture. Having time with your friends is important too -- help him feel reassured about what you do when you're out with the girls. Talk openly about your plans, and include him in fun plans too. Decide together where you'll go and what you'll do. That way, you can both feel better about your social life, your relationship -- AND your parenting.