I think I should have lied to my now ex that I didn't love her due to me not being able to
Why do you think that you should have lied to her?
I think a relationship needs a foundation of lies
If you don't love someone, you should not tell them that you do. Lying to someone about how you feel is hurtful and will only leave you with regrets in the future.
If I had lied to her I could have kept her happy.
She would not have been truly happy in a relationship based on lies. It is better to have a truthful and honest relationship.