So ive had nexplanon for 2 years now and i also use condoms while having sex. what's the chance of pregnancy?

Very small: The Nexplanon is an extremely reliable method of contraception but nothing is 100%. The failure rate ( risk of pregnancy) rises some with obesity but remains less than 0.05%. The condoms are a very good idea in order to decrease the risk of STDs but aren't necessary for contraception. You are to be commended for using both as is recommended. It is very responsible of you. Hope this helps.