Sustenance can refer to any means of subsistence or livelihood.
I am sorry to hear about your challenge. If both of you are dedicated to the marriage, inshallah you will find a way to make it work and maybe you will both eventually find greater ease through working together to build your life financially and otherwise.
If the person has good faith and religious piousness with good manners then don't refuse his marriage proposal. Sustenance is in the hands of Allah (SWT) and He grants sustenance to all His creatures. The marriage itself is a way to get more sustence as the Hadeeth says: Get married for getting more sustenance, verily the wife will bring blessed sustenance تزوّجوا للرزق فإنّ فيهنّ بركة.
Hadeeth says: Allah created the souls of people 2000 years before creating their bodies, and He created their sustenance 2000 years before creating their souls.
Allah (SWT) Has granted enough sustenance for all His creatures, but arrogant people snatch away the rights of others causing them to be hungry. Ameerul Mo'minnen Ali (AS) said: No one becomes hungry but only because someone else has taken away his right. ما جاع فقير إلا بما منع به غني
The real cause of the poverty is the injustice done by wrong doers on others.
There are multiple supplications which are known to provide the blessing of sustenance/الرزق. However, amongst the most distinguished of these supplications is the dua that is highly recommended to be recited after Ishaa prayer; تعقيب صلاة العشاء
Abeed Ibn Zurara narrates that he was in the company of Imam Jafar Asadiq (a.s) while a poor man complained to the Imam (a.s) about his bad financial status and for a solution out of it. The Imam (a.s) replied "If you have completed your Ishaa prayer then say "O Allah! Verily, I lack acquaintance with the place of my sustenance; rather, I am seeking it owing to ideas that come upon my mind. I consequently wander in places searching for it. By doing such, I am as confused as the confounded, since I do not know whether my sustenance lies in a plain, on a mountain, on the ground, in the air, on lands, in seas, at whose hands, or who the source of it is. I have full knowledge that You know all these, the causes of them are in Your Hands, and it is You Who distribute it out of Your compassion and cause it out of Your mercy. O Allah, please send blessings to Muhammad and his Household and make, O Lord, Your sustenance that is provided (by You) to me expansive, my seeking for it easy for me, and its source close to me. Please, do not fatigue me by seeking that which You have not decided for me to take, because You are certainly in no need for tormenting me while I am in full need for Your mercy. [Please] send blessings upon Muhammad and his Household and confer liberally upon me, Your slave, out of Your graciousness. You are surely the Lord of great favor.”
اللهم إنه ليس لي علم بموضع رزقي، وإنما أطلبه بخطرات تخطر على قلبي فأجول في طلبه البلدان، فأنا فيما أنا طالب كالحيران، لا أدري أفي سهل هو أم في جبل أم في أرض، أم في سماء أم في بر أم في بحر، وعلى يدي من ومن قبل من؟ وقد علمت أن علمه عندك وأسبابه بيدك، وأنت تقسمه بلطفك وتسببه برحمتك، اللهم فصل على محمد وآله، واجعل يا رب رزقك لي واسعا، ومطلبه سهلا، ومأخذه قريبا، ولا تعنتني بطلب ما لم تقدر لي فيه رزقا، فإنك غني عن عذابي، وأنا فقير إلى رحمتك، فصل على محمد وآل محمد، وجد على عبدك بفضلك، إنك ذو فضل عظيم
Abeed Ibn Zurara concludes the narration by stating that not too much time passed until this same poor man became blessed with sustenance.
Of course it's important to note that one condition for this dua or any to be answered- is to have genuine faith in Allah (swt) and to satisfy His requests first before expecting Him to satisfy ours.
Hadith: Bihar Anwar V 83 Pg 124
as salam alaikum
the Qur'an says: "Seek your sustenance from Allah and serve Him" (29:17).
It also says: "He (Allah) does not command you to take the angels and prophets as your Lords ("Arbab", plural of "Rabb"). Would He command you disbelief after you have submitted yourselves (to Allah)?".
It follows that an Imam also is not a Rabb and that only Allah is the Cherisher and Sustainer of the whole creation.
With prayers for your success.