Poly Relationships

So I want to preface this by saying that I've never been in a relationship before, hell I've never even kissed anyone before.

Recently 2 very good friends of mine (who are dating) came to me, they said that they had both agreed that they would like me to join their relationship. I was a bit flustered and told them that I was not looking to be in a relationship as my mental health is not great at the moment (which is true). I told them that I'd have to think it over for a while even when my mental health gets better.

My question is, should I get into this relationship (when I get better), or should I be in a relationship with 1 person before I tackle 2 people?