can u still be friends with your ex?

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i had this friend who told me he can never be friends with his ex because the pain that was brought in their relationship was unbearable, he maybe said so because their relationship ended not in a nice way, the relationship lasted for 7 years and his gf got impregnated with another guy. The only reason why the girl got into an awkward situation was because my friend dont have much time with her. He told me he can forgive his gf but they can never be friends again.Considering the number of years of the relationship and the reason of the break-up. If you were on my friend's shoes will you do the same? I mean you will forgive him/her but can u still be friends with your ex?