Should I text her

I love this girl and we used to date 2 years ago, but we broke up and she has been dating the same guy since then. They seem very happy and good together, but may be going through a rough patch right now.

I want to get back together with her, but i know that if i push it while she still has a boyfriend she'll end up not talking to me at all.

We have texted and snapped a few times since the breakup, primarily within the past month, and it all went well. How should i start another conversation with her and keep it going? Also how can i get the balls to keep messaging her?