Please, I have something bothering me about my relationship. I have been dating my spouse for a year and half now, but he has been asking for sex recently, and I don't wish to engage in such act. For now we can't afford money for our wedding. My question is: can I go ahead, have my parents' blessing for marriage and move on with my life; then later we can have a proper wedding? Is it a sin to have sex after the parents blessed your marriage but before going to the altar?
You are trying to find loopholes in God's law. You refer to your boyfriend as your "spouse," but that word is for a married couple. You do not have a spouse because you are not married.
Your boyfriend is wanting to violate God's law regarding sex being only allowed in marriage (Hebrews 13:4). That is a warning sign: he values his desires more than he values God. It also tells me that he is impatient; and that you two have been involved in sexual behavior (lewdness), even though it hasn't gotten to the point of intercourse yet. "Let us behave properly as in the day, not in carousing and drunkenness, not in sexual promiscuity and sensuality, not in strife and jealousy. But put on the Lord Jesus Christ, and make no provision for the flesh in regard to its lusts" (Romans 13:13-14). These are hints that you might not have picked the best man to be your husband.
A plan for a wedding is not a marriage. Sex at this point would still be fornication. If you can't wait then have a cheap civil marriage now and have a fancy wedding later.