Wa alaikum salaam wa rahmatulahi wa barakatuh,
It certainly does sound like you have found your ideal life partner, but yet you also realize that your actions with him are not permissible and have done everything you can to make matters as core tabs you can regarding cutting contact and having pure intentions.
Regarding the fiqhi matters, you should seek some advice from someone of knowledge to find out if your plans are Islamically acceptable, but there are also some other matters you should keep in mind. For now, until you marry, neither of you are obliged to stay committed to your agreement. He is free to marry someone else, as are you. You both have needs that can be fulfilled in marriage and cannot otherwise. You may find waiting for a period of time you will face temptations and the only way to overcome this is to get married. Essentially, you need to be prepared that things may not go to your plan. Of it is this man you wish to be with and you dot want him to.marry another or for you to be tempted, and someone of knowledge advises you that it is permissible for you to marry him, then you do not have to wait and should move forward with it to avoid complications that will come of waiting.
It is always advisable in these situations to pray istikhara and ask Allah to guide you to what is best for you and most pleasing to Him. However, you must be aware that having had contact with this man already you have already established feelings towards him which will cloud your judgments more favorably. Therefore, it would also be wise to seek the advice of a loved one who will be able to advise you from a neutral standpoint.
If it turns out that you would like to take matters further, then ensure to do it in a good way from the start. Meet with him and his family with you and yours so that you can get to know him properly in an acceptable way as well has had the input of your families also. You can do this by asking someone in your family to contact him or someone on his so that you do not need to talk with him directly.
Aside from this, keep Allah close and He will surely guide you in the right direction and turn your heart away from this man if he is not right for you. Being close to Allah will bring you contentment in whatever the final outcome is. It is also important to continue to repent to Allah for the sins you committed with this man and Allah loves to give. This will be a way to purify your heart from what had happened. Part of this repentance includes abstaining from committing the same sins again by cutting contact with this man, which alhamdulillah, is what you have been doing already.
May Allah guide you on the straight path and grant you a righteous spouse who will be the comfort of your eyes in this life and the next.
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