Can I be friends with a married coworker?

I (31m) am friends with a coworker (30f). But she's married, I have a girlfriend. Is it an issue if we are friends? We usually just friendly joke around nothing flirtatious and text about nonsense in the office and other coworkers. Are we crossing the line? It is clear she loves her husband and would never ever cheat on him, and I love my girlfriend and would never cheat.
Can I be friends with a married coworker?
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