DOES HEAVEN EXIST?
Yes for two reason:
The first reason is proof for myself: I have been there and need no other proof. But I don't expect you to believe Heaven exists merely because someone says they've been to Heaven. Therefore, the second reason is what should be most important to you.
The second reason is that Heaven (a place where our spirit - our soul- will reside eternally in the presence of God's light and love and all that is good) exists because God created us to be with Him eternally as a reward for obeying His divine and natural laws. Our powers of reason tell us that when God created us, He had a purpose, and being infinitely good, that purpose was to enable us to share in His love, His light, His beauty, His power, His grace, and in everything that is possible for Him to share with us. If you had a banquet with tables filled with all the best foods in the world, you would want to share them with your children - because you love them completely. God's being is more than a banquet of the best foods in the world, God's being is filled with infinitely more superior things. God's being is filled with infinite love and all things good - AND - we "are" His children.
Some have seen God face-to-face and have received a taste of God's infinite light, love, beauty, power, and so forth, but the glimpse can only be temporary, and that is because the person who is experiencing God face-to-face is a temporal being, and as such, cannot have an eternal experience without leaving the temporal existence. To experience God eternally, one must permanently leave the spatio-temporal universe, since God exists in the eternal spiritual universe and is incompatible with the spatio-temporal universe. That is because God cannot exist within what He created. Therefore, Heaven - being in God's presence eternally - exists in the "other universe", the spiritual universe reserved for those who love God, and in this life, only a glimpse is possible.
Consequently, because God is infinitely just and infinitely merciful, our powers of reason tell us that an infinitely intelligent being had to have a just reason for creating us, and that reason is to reward those who exercise their will in obeying Him, and to reject those who defy His will (who will thereby suffer the loss of His love, light and infinite goodness).
Please review what I have written about God in other parts of this website for additional proofs regarding God's attributes which give an added dimension for the proof of the existence of Heaven, because the more you know about God, the closer you will be to Heaven, and the more your doubts will evaporate.